W. H. Hudleston — On the Yorkshire Oolites. 53 



the representative of a section of the group. This form is recog- 

 nized by Tate and Blake (Yorkshire Lias, p. ool) as occurring both 

 in the highest beds of Alum Shale (Upper Lias), and also in the 

 Blue Wyke Beds {i.e. the Dogger Sands). 



It may be conceded to palteontologists who are fond of " making 

 species " that fairly well marked natural form-groups existed in 

 times past as they do now ; but a " species " as it existed in Nature 

 is probably in many cases a very different thing from a "species" 

 ci-eated by an author, who only obtains a glimpse of the facts. 

 Hence T am bound to confess my belief that very many " species " 

 must be regarded as more or less provisional arrangements which 

 an extended knowledge of the facts will tend greatly to modify. La 

 the case of the fossils now more especially under consideration 

 we may seek to find names for them in the various foreign books, 

 straining a point here and there to make things fit, and v/heu this 

 resource fails us, we may confess defeat by making a new species. 

 Where the differences are considerable and not bridged over by 

 intermediate forms, this is perfectly legitimate. In dealing with the 

 selected specimens of what I have called the muricatim-gvon^, it 

 seems the best plan to regard them as tending to arrange themselves 

 in two sections, more especially as no great regularity of difference, 

 BO system as it were, seems traceable. 



Description, etc., of selected specimens (Fig. 1). — Specimen from 

 the Dogger (zone 1), Peak (Blue Wyke). Collection of Sowerby's 

 types, British Museum. Marked " E. H. Bay." 



Length (restored) 20 milKmetres. 



Width 6 



Height of whorl to width ^ . , , 3-5:5. 



Spiral angle 16°. 



Spirals 4, except in the last two whorls, where a fifth spiral is 

 partially developed ; longitudinals straight, with very slight inclina- 

 tion, and rather wide apart. 



Fig. 2. — Specimen from the Dogger (zone 1), Peak (Blue Wyke). 

 Leckenby Collection. 



Length (restored) 18 millimetres. 



Width i 6 ,, 



Height of whorl to width 3 : 4*5 



Spu-al angle , 17°. 



About an average width : spirals 5 on all the whorls as far as can 

 be counted : longitudinals curved, with slight inclination, and rather 

 close together. 



Figures 1 and 2 may be regarded as more or less typical of the 

 two commonest varieties of G. miiricatum, and very nearly the same 

 two varieties may be noted in the Coralline Oolite of Pickering. In 

 the "Corallian Gasteropoda" (Geol, Mag. 1880, p. 402) these_ two 

 A^arieties were described as G. miiricatum, Sow., and G. Bussiense, 

 D'Orb., the latter being the form with 4 spirals. In the Dogger 

 Sands specimens with 5 spirals and curved costae are tolerably 

 numerous, and except that they mostly run rather larger, many must 



V In this measurement the penultimate is selected. 



